Deleting voicemail messages after 3 or more days

Hi all,

i’m italian, sorry for my poor english.

I want that my trixbox server delete voicemail messages not immediately, but only after 3 or more days.

How do i have to set freepbx in order to reach this result?

I suppose i have to set adequately the “VM Options” field in the extension option, but i don’t know how…

Thanks - Daniele